Valve Cover Gasket Leak

Most Likely Causes

1. 1

   Age and heat hardening

   The valve cover gasket seals the top of the engine where the valve cover bolts to the cylinder head. The rubber gasket hardens from constant heat and eventually loses its ability to seal. This is normal wear on any engine and becomes common after 80,000-100,000 miles or 10 or more years of service.

2. 2

   Over-tightened or under-tightened cover bolts

   Valve cover bolts must be torqued evenly to spec — typically 6-9 ft-lbs for most engines. Over-tightening crushes and distorts the gasket, creating leak paths. Under-tightening allows the cover to flex and lose the seal. Always torque to specification in a criss-cross pattern.

   Many DIYers over-tighten valve cover bolts. Use a torque wrench.

3. 3

   Crankcase overpressure from PCV failure

   A blocked or failed PCV valve allows crankcase pressure to build and push oil past the valve cover gasket. If the gasket leak appeared suddenly or the engine is blowing oil from multiple locations, check the PCV valve before replacing gaskets.

4. 4

   Spark plug tube seals leaking

   On many engines, the valve cover contains rubber tube seals around each spark plug well. When these seals fail, oil enters the spark plug wells and soaks the coil boots, causing misfires. Oil in a spark plug well is often noticed first when changing spark plugs.

   Spark plug tube seal kits are included with most valve cover gasket sets.

How to Diagnose It

1. 1

   Visual inspection of the valve cover seam

   Clean the engine top with degreaser. After a short drive, inspect the seam where the valve cover meets the cylinder head with a flashlight. Fresh oil seeping from this seam confirms a valve cover gasket leak. Check all four sides of the cover including the front and rear corners which are the most common failure points.

   Tool: Degreaser, flashlight

2. 2

   Spark plug well oil check

   Remove the ignition coil from each cylinder and look inside the spark plug well with a flashlight. Oil pooled in the well means the spark plug tube seal has failed. The amount of oil indicates how long the seal has been leaking. This also explains any cylinder-specific misfire codes.

   Tool: Flashlight

3. 3

   PCV valve check

   Test the PCV valve by removing and shaking it. A healthy valve rattles freely. A stuck valve will not rattle or feels stiff. Also check the PCV hose for cracks or blockage. A failed PCV system is a frequent contributor to valve cover gasket leaks.

How to Fix It

• Replace valve cover gasket

  Remove any components blocking access to the valve cover (typically ignition coils, PCV hose, and a few other connections). Remove the cover bolts evenly, lift the cover, and peel off the old gasket. Clean both mating surfaces with a plastic scraper and brake cleaner. Install the new gasket (with or without sealant at corners per instructions), reinstall the cover, and torque bolts to spec in a criss-cross pattern from center outward.

  Valve Cover Gasket Set (includes Spark Plug Tube Seals)↗RTV Sealant For Corners If Specified↗

• Replace spark plug tube seals

  Most valve cover gasket kits include replacement spark plug tube seals. Always replace these at the same time as the gasket since they are accessible and labor is already performed. Press new seals into the valve cover bore before reinstallation. Remove and inspect spark plugs while access is open — if oil-soaked coil boots caused misfires, inspect or replace the plugs and boots.

  Spark Plug Tube Seals (usually Included In Gasket Kit)↗Spark Plugs (if Oil-fouled)↗

• Replace PCV valve

  Replace the PCV valve whenever doing a valve cover gasket job since the valve is typically attached to or near the cover. A fresh PCV valve prevents crankcase pressure from blowing out the new gasket.

  PCV Valve↗